In the context of the fight against fraud in the sphere of secondments, the Belgian legislator has given the courts, the social security authorities and the social inspectorate the ability to set aside an A1 certificate issued by another Member State confirming that a worker was subject to its social security regime, in the event of abuse. 

On 11 July 2018, in the case of the European Commission -v - Kingdom of Belgium (C-356/15) the ECJ ruled that national laws that make it possible to undermine an A1 certificate by unilaterally subjecting a worker to its social security legislation, are not compatible with the principle of sincere cooperation between Member States. 

Therefore, the Belgian courts may only unilaterally set aside an A1 certificate within the narrow limits set out in the Altun case (see Update from April 2018)

Sophie Maes, partner at Claeys & Engels